Is there any difference between these setups other than the number of sats? I thought I read somewhere that the 621s have have the sub. I'm asking because I need to upgrade my speakers, primarily for music, and a 4 sat system just wont work so well in my apartment. If my concern about the 621s is correct, does anyone have a suggestion for loud, bass-strong speakers for under $200 that will be used primarily for music with gaming as a secondary(and almost insignificant) concern?